What text structure do you think the article “disappearing bees threaten ice cream sellers” will use? a. narrative c. expository b. descriptive d. persuasive

C <<<< answer the way you have written it. 
Second one of the top <<<<< same answer expository

That's a pretty big jump to go from bee disappearance to ice cream sellers. Any time you have a jump that large where you cannot easily see the connection, you get something exposity to begin with. 

Since you are not giving any other clue, the answer should be expository. If the author goes on to wanting his reader to do something then the answer would be persuasive. "We should protect bees from disappearing because if we don't, ice cream sellers will also become a thing of the past" would be an example of persuasive.

You could write this as a narrative. You could tell the story of one ice cream seller, but we have not been given a clue to suggest that, and descriptive -- I just don't see the connection. I don't see how it would help get to the point.

The answer is still expository. You need to explain the connection between ice cream sellers and bee disappearance.

The answer is holding on to the past